1. Technical Field
Example embodiments relate to an electrostatic discharge protection circuit and more particularly to an electrostatic discharge protection element in a semiconductor memory device.
2. Description of the Related Art
An electrostatic discharge (ESD) is a momentary electric current which flows between two objects having different electrical potentials caused by a direct contact or induced by an electrostatic field.
Semiconductor memory devices may include ESD protection circuits between an input/output (I/O) pad and an internal circuit to prevent the ESD from damaging isolation layers and channel regions formed in the internal circuit.
The ESD may destroy an element, an oxide layer, and a metal wiring which are included in the internal circuit. For example, a high electric current and electronic field may cause a Joule heat in contact regions of the internal circuit, and a second breakdown due to the Joule heat may cause damage to the internal circuit elements. As very-large scale integration (VLSI) circuits become smaller, the oxide layer therein also become thinner, and thus the oxide layer may be easily deteriorated by sudden high electric current, such as that caused by ESD. In addition, the metal wiring becomes thinner, and thus the metal wiring may be easily destroyed due to the high operational temperature, such as that caused by ESD.
Operational characteristics of the damaged internal circuit elements may be degraded such that an ESD threshold voltage may become lower and a leakage current may increase, and thus the damaged internal circuit elements will not be able to perform desired operations under such conditions.
As the semiconductor device becomes smaller, the oxide layer becomes thinner, and thus an improved function for ESD protection is highly recommended.